1. Field of the Invention
The present invention is related to a printed circuit board with a built-in capacitor and a manufacturing method thereof, particularly, related to a printed circuit board, which is excellent in electrical characteristics and high density, and a manufacturing method thereof.
2. Description of the Related Arts
In recent years, demand for a printed circuit board is increasing year by year so as to cope with higher density and higher frequency as an electric apparatus is advanced to high density and high speed. Miniaturizing a component is advanced so as to make mounting density of a printed circuit board higher. However, miniaturizing more than a current level almost reaches the limit in consideration of mounting yield. Further, mounting design of a printed circuit board is getting harder extremely due to conditions of allocating a bypass capacitor, which should be mounted in the neighborhood of a terminal of IC.
In the past, a passive electronic component such as capacitor and resister is connected electrically to a printed circuit board by solder mounting. However, in view of the above-mentioned requirement, recently, a method of forming an interlayer capacitor that is constituted by a material having high permittivity, which is used as an interlayer insulative film of printed circuit board, and another method of filling up an interlayer of printed circuit board with a material having high permittivity locally and utilizing as an interlayer capacitor has been proposed (for example, Japanese Patent Application Laid-open Publication Nos. 2001-15928 and 9-116247/1997).
However, in the case of the former method, permittivity of the insulative film (layer) that is used in the interlayer is uniform, so that a capacitance value is essential to be adjusted by its area when a different capacitance value is required. Therefore, the method is disadvantageous to a degree of freedom from limitation based on designing or high density. Consequently, such an interlayer capacitor is merely used for a capacitor for noise reduction.
In the case of the latter method, as disclosed in the Patent Publications mentioned above, an opening of which area is equivalent to a required capacitance value is formed on a layer, which is composed of a material having low permittivity, by a CO2 laser or the photo-etching method. The opening is filled up with a material having high permittivity, and then a local capacitor is formed.
In this case, however, a gap generates at an interface between the materials having high permittivity and low permittivity respectively due to hardening contraction when hardening the material having high permittivity and different thermal expansion rates between the materials having high permittivity and low permittivity. Consequently, there existed problems such that a conductive material penetrates into the gap and resulted in short-circuiting a lower electrode and an upper electrode and failing to function as a capacitor, and the interlayer capacitor is less in reliability. In the particular case, there existed a further method of forming a dielectric layer by a dry process such as the sputtering method so as to improve adhesiveness of the interface between the layers constituted by the materials having high permittivity and low permittivity respectively. However, the further method is disadvantageous to productivity and processing cost.
Accordingly, in consideration of the above-mentioned problems of the prior arts, an object of the present invention is to provide a printed circuit board, which is high in mechanical strength, reliability and capacitance accuracy and further low in manufacturing cost, and a manufacturing method thereof
In order to achieve the above object, the present invention provides, according to an aspect thereof, a manufacturing method of a printed circuit board comprising steps of: forming a pattern of lower electrode at a portion to be formed with a capacitor element on a substrate; forming a capacitor insulative layer constituted by a paste material having high permittivity selectively at a position corresponding to the lower electrode; forming an interlayer insulative film having low permittivity all over the entire surface of the substrate including the capacitor insulative layer; exposing the capacitor insulative layer by grinding the surface of the interlayer insulative film so as to be flat; and forming a capacitor element by forming a pattern of upper electrode on the surface of the capacitor insulative layer.
According to another aspect of the present invention, there provided a printed circuit board composed of: a substrate; a lower electrode formed with a pattern at a portion to be formed with a capacitor element on the substrate; a capacitor insulative layer of a paste material having high permittivity formed selectively at a position corresponding to the lower electrode; an interlayer insulative film having low permittivity formed all over the entire surface of the substrate including the capacitor insulative layer; and an upper electrode constituting a capacitor element formed with a pattern on the surface of the capacitor insulative layer that is exposed by grinding the surface of the interlayer insulative film so as to be flat.
Other object and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.